Optical information-recording medium manufacturing method and manufacturing apparatus

ABSTRACT

A method of manufacturing an optical information recording medium that has a substrate having a signal recording layer formed on one principal surface thereof; and an optically transparent layer formed on the signal recording layer and made from a radiation cure type resin. According to the method, when the optically transparent layer is formed, the radiation cure type resin is supplied onto the substrate, and the radiation cure type resin is applied over the substrate by spinning the substrate at a predetermined number of application revolutions in a spin coating method. The number of revolutions of the substrate is increased after the application of the resin, and radiation is irradiated to cure the radiation cure type resin while the number of revolutions of the substrate is increased.

TECHNICAL FIELD

[0001] The invention relates to a technique for manufacturing an opticalinformation recording medium and specifically to a method of and anapparatus for manufacturing an optical information recording medium thathas a very uniform optically transparent layer.

BACKGROUND ART

[0002] In recent years, various types of optical recording have beeninvestigated in the field of information recording. In the opticalinformation recording system, recording/reproducing can be made at highdensity and low cost with a non-contact mechanism, and its applicationshave now become widespread. At present, for example, an availableoptical disk has a structure in which an information layer is formed ona transparent resin substrate with a thickness of 1.2 mm and protectedby an overcoat; or a structure in which two transparent resin substrateseach with a thickness of 0.6 mm and an information layer provided on oneor both sides of the substrate are bonded to each other.

[0003] In recent years, the way to increase the recording density of theoptical disk has been investigated, for example, including increasing anumerical aperture of objective lens and shorting a wavelength of alaser beam. If the substrate on the recording/reproducing side (thesubstrate on the incident laser beam side) has a relatively smallthickness, the laser beam spot can be less affected by aberration, andtherefore, the disk can have a relatively large tolerance for theinclination angle (tilt). From this point of view, it has been proposedthat the recording/reproducing side substrate should have a thickness of0.1 mm, the NA be about 0.85 and the laser beam have a wavelength ofabout 400 nm. Under such conditions, variations in thickness of therecording/reproducing side substrate should preferably be controlled to5% or less, in terms of the influence of recording/reproducing light onfocus or spherical aberration.

[0004] A potential way to control the variations in thickness to such asmall value may include bonding substrate sheets each having a uniformthickness of a few tens of Am to each other with a radiation cure typeresin. However, the process using such substrate sheets is veryexpensive. Therefore, a spin coating method should preferably be used toform the base material only from a radiation cure type resin on therecording/reproducing side.

DISCLOSURE OF THE INVENTION

[0005] The process of forming the recording/reproducing side substrate(optically transparent layer) in a spin coating method has difficulty inmaking the thickness uniform ranging from the inner radius to the outerradius. Specifically, the thickness tends to be made small at the innerradius and significantly large at the outer end. If a radiation curetype resin on the substrate being rotated is cured by radiation for thepurpose of making the thickness uniform in the vicinity of the outerend, burrs can be generated at the periphery portion, which can lead toproblems with the mechanical characteristics and the appearance.

[0006] Against the above problems, it is an object of the invention toprovide a method of manufacturing an optical information recordingmedium, in which a uniform optically transparent layer can be formed. Itis another object of the invention to provide a method of manufacturingan optical information recording medium, in which burrs can be preventedfrom being generated at the outer end of the substrate.

[0007] In a first aspect of the invention, provided is a method ofmanufacturing an optical information recording medium that has asubstrate having a signal recording layer formed on one principalsurface thereof; and an optically transparent layer formed on the signalrecording layer and made from a radiation cure type resin. According tothe method, when the optically transparent layer is formed, theradiation cure type resin is supplied onto the substrate, and theradiation cure type resin is applied over the substrate by spinning thesubstrate at a predetermined number of application revolutions in a spincoating method. The number of revolutions of the substrate is increasedafter the application of the resin, and radiation is irradiated to curethe radiation cure type resin while the number of revolutions of thesubstrate is increased.

[0008] In a second aspect of the invention, provided is a method ofmanufacturing an optical information recording medium that has asubstrate having a signal recording layer formed on one principalsurface thereof; and an optically transparent layer formed on the signalrecording layer and made from a radiation cure type resin. According tothe method, when the optically transparent layer is formed, theradiation cure type resin is supplied onto the substrate, and theradiation cure type resin is applied over the substrate by spinning thesubstrate at a predetermined number of application revolutions in a spincoating method. The number of revolutions of the substrate is increasedto a predetermined number of revolutions that is greater than thepredetermined number of application revolutions after the application ofthe resin, and the predetermined number of revolutions for apredetermined period is maintained after the number of revolutionsreaches the predetermined number of revolutions. Radiation is irradiatedto cure the radiation cure type resin while spinning the substrate atthe predetermined number of revolutions, after the number of revolutionsreaches the predetermined number of revolutions.

[0009] In a third aspect of the invention, provided is a method ofmanufacturing an optical information recording medium that has asubstrate having a signal recording layer formed on one principalsurface thereof; and an optically transparent layer formed on the signalrecording layer and made from a radiation cure type resin. According tothe method, when the optically transparent layer is formed, supplyingthe radiation cure type resin onto the substrate is started whilespinning the substrate at a speed lower than a predetermined speed.Applying the radiation cure type resin over the substrate is startedwhile spinning the substrate at a speed higher than the lower speed.Then the supplying the radiation cure type resin is stopped, and thenthe applying the radiation cure type resin is stopped.

[0010] In a fourth aspect of the invention, provided is a method ofmanufacturing an optical information recording medium that has asubstrate having a signal recording layer formed on one principalsurface thereof; and an optically transparent layer formed on the signalrecording layer and made from a radiation cure type resin. According tothe method, when the optically transparent layer is formed, theradiation cure type resin is supplied onto different portions located atsubstantially the same radius inside the region where the signalrecording layer is formed. The supplied radiation cure type resin isapplied over the substrate by spreading the supplied radiation cure typeresin.

[0011] In a fifth aspect of the invention, provided is a method ofmanufacturing an optical information recording medium that has asubstrate having a signal recording layer formed on one principalsurface thereof; and an optically transparent layer formed on the signalrecording layer and made from a radiation cure type resin. According tothe method, when the optically transparent layer is formed, supplied isthe radiation cure type resin in the shape of a ring at substantiallythe same radius inside the region where the signal recording layer isformed. The supplied radiation cure type resin is applied over thesubstrate by spreading the supplied radiation cure type resin.

[0012] In a sixth aspect of the invention, provided is a method ofmanufacturing an optical information recording medium that comprises asubstrate having a central hole and a signal recording layer formed onone principal surface thereof; and an optically transparent layer formedon the signal recording layer and made from a radiation cure type resin.According to he method, the radiation cure type resin is supplied ontothe substrate, and the supplied radiation cure type resin is spread andapplied over the substrate, thereby forming the optically transparentlayer. During the supplying the radiation cure type resin, the centralhole is blocked with a member having a sealing to prevent the radiationcure type resin from leaking into at a portion adjacent to thesubstrate.

[0013] In a seventh aspect of the invention, provided is a method ofmanufacturing an optical information recording medium that has asubstrate having a signal recording layer formed on one principalsurface thereof; and an optically transparent layer formed on the signalrecording layer and made from a radiation cure type resin. According tothe method, radiation is irradiated to cure the radiation cure typeresin while spinning the substrate. When the radiation is irradiated, anend face portion of the substrate is placed in an atmosphere containingan excess amount of oxygen.

[0014] In an eighth aspect of the invention, provided is a method ofmanufacturing an optical information recording medium that comprises asubstrate having a signal recording layer formed on one principalsurface thereof; and an optically transparent layer formed on the signalrecording layer and made from a radiation cure type resin. According tothe method, radiation is irradiated to cure the radiation cure typeresin while spinning the substrate, and a burr is removed from an outerend face portion of the substrate after the radiation cure type resin iscured.

[0015] In a ninth aspect of the invention, provided is a method ofmanufacturing an optical information recording medium that has asubstrate having a signal recording layer formed on one principalsurface thereof; and an optically transparent layer formed on the signalrecording layer and made from a radiation cure type resin. According tothe method, the radiation cure type resin is applied onto the signalrecording layer in a spin coating method; and radiation is irradiated tocure the radiation cure type resin while spinning the substrate, so thatthe optically transparent layer is formed. A predetermined member isplaced so as to be substantially in contact with the outer end of theprincipal surface while the substrate is spinning.

[0016] In a tenth aspect of the invention, provided is a method ofmanufacturing an optical information recording medium that comprises asubstrate having a signal recording layer formed on one principalsurface thereof; and an optically transparent layer formed on the signalrecording layer and made from a radiation cure type resin. According tothe method, the radiation cure type resin is applied on the signalrecording layer in a spin coating method; and radiation is irradiated tocure the radiation cure type resin while spinning the substrate, so thatthe optically transparent layer is formed. A high pressure gas jet isapplied to at least one portion of the outer end of the principalsurface while the substrate is spinning.

[0017] In an eleventh aspect of the invention, provided is an apparatusfor manufacturing an optical information recording medium that comprisesa substrate having a signal recording layer formed on one principalsurface thereof; and an optically transparent layer formed on the signalrecording layer and made from a radiation cure type resin. The apparatusincludes a unit that supplies the radiation cure type resin, a unit thatspins the substrate to apply or spread the radiation cure type resin, aunit that irradiates radiation while the substrate is spun to form theoptically transparent layer; and a unit that suppresses the generationof burrs at a periphery of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a diagram for illustrating a method of manufacturing anoptical information recording medium, which specifically shows a timingof a process of curing the resin while the rotation of the substrate isaccelerated.

[0019]FIG. 2 is a diagram showing a configuration of an apparatus forcarrying out the method of manufacturing the optical informationrecording medium according to the invention.

[0020]FIGS. 3A to 3C are diagrams for illustrating a method ofmanufacturing the optical information recording medium.

[0021]FIGS. 4A and 4B are time charts each showing a timing of eachprocess in the method of manufacturing the optical information recordingmedium.

[0022]FIG. 5 is a diagram illustrating a mechanism for pulling a capdownward (a mechanism having a suction hole at the center of a rotarytable).

[0023]FIGS. 6A to 6C are diagrams illustrating other examples of themechanism for pulling the cap downward (with a magnet).

[0024]FIG. 7 is a diagram for illustrating a process of curing theradiation cure type resin by irradiating radiation;

[0025]FIGS. 8A to 8C are diagrams each showing an optically transparentlayer irregularly formed on the optical information recording medium.

[0026]FIG. 9 is a diagram illustrating a timing of the radiationirradiation in the process of curing the radiation cure type rein afterthe acceleration of the rotation.

[0027]FIGS. 10A and 10B are diagrams illustrating burrs generated at theperiphery of the substrate of the optical information recording medium.

[0028]FIG. 10C is a diagram illustrating a method of removing burrs witha laser beam.

[0029]FIG. 10D is a diagram illustrating a method of removing burrs witha cutter.

[0030]FIG. 11A is a diagram showing an optical information recordingmedium having a hard coat formed on the optically transparent layer.

[0031]FIG. 11B is a diagram showing an optical information recordingmedium which is formed after the process of forming the opticallytransparent layer and then removing a cap.

[0032]FIG. 12 is a diagram showing a radius-dependency of the thicknessof the optically transparent layer in the optical information recordingmedium manufactured by the method according to the present invention.

[0033]FIG. 13A is a top plan view showing a nozzle for supplying theradiation cure type resin onto the substrate according to the invention.

[0034]FIG. 13B is a sectional view (along A-A′) showing the nozzle forsupplying the radiation cure type resin onto the substrate according tothe invention.

[0035]FIG. 13C is a perspective view showing the nozzle for supplyingthe radiation cure type resin onto the substrate according to theinvention.

[0036]FIG. 14A is a top plan view showing another nozzle for supplyingthe radiation cure type resin onto the substrate according to theinvention.

[0037]FIG. 14B is a sectional view (along A-A′) showing the anothernozzle for supplying the radiation cure type resin onto the substrateaccording to the invention.

[0038]FIG. 14C is a perspective view showing the another nozzle forsupplying the radiation cure type resin onto the substrate according tothe invention.

[0039]FIG. 15 is a time chart for the method of manufacturing theoptical information recording medium, in which processes of supplying,applying, and curing the resin are independently performed in differentplaces.

[0040]FIG. 16 is a diagram showing a configuration of an apparatus forcarrying out the method of manufacturing the optical informationrecording medium, in which the processes of supplying, applying, andcuring the resin are independently performed in different places.

[0041]FIG. 17 is a diagram illustrating a mechanism for holding theoptical information recording medium to be transferred.

[0042]FIG. 18 is a diagram illustrating a system for suppressing thegeneration of burrs at the outer end of the substrate;

[0043]FIGS. 19A to 19C are diagrams for illustrating a method ofmanufacturing the optical information recording medium, in which thegeneration of burrs can be suppressed;

[0044]FIGS. 20A to 20C are diagrams illustrating burrs generated at theperiphery of the optical information recording medium.

[0045]FIGS. 21A and 21B are diagrams each showing the shape of a memberfor removing burrs generated at the outer end (a burr-removing member).

[0046]FIG. 21C is a diagram showing the shape of a burr-removing memberviewed from the outer end to the center of the substrate.

[0047]FIG. 22A is a top plan view showing a burr-removing member in theshape of a circular cylinder.

[0048]FIG. 22B is a sectional view showing a burr-removing member in arectangular shape placed adjacent to the substrate.

[0049]FIG. 22C is a top plan view showing the burr-removing member inthe rectangular shape placed adjacent to the substrate.

[0050]FIG. 22D is a sectional view showing a burr-removing member in anarc shape placed adjacent to the substrate.

[0051]FIG. 23A is a diagram illustrating a configuration in which ashielding plate is placed above the burr-removing member when the resinis cured.

[0052]FIG. 23B is a diagram showing the shielding plate.

[0053]FIG. 24A is a diagram for illustrating a manufacturing process ofan information recording medium having a protective layer formed on theoptically transparent layer.

[0054]FIG. 24B is a diagram showing a structure of the informationrecording medium obtained after the process of forming the protectivelayer on the optically transparent layer and then removing a cap;

[0055]FIG. 24C is a diagram showing an optical information recordingmedium having a plurality of signal recording layers;

[0056]FIG. 25A is a diagram showing a burr-removing member in the shapeof a cord placed adjacent to the substrate;

[0057]FIG. 25B is a diagram showing a configuration in which thecord-shaped burr-removing member is formed into an annular ring andplaced adjacent to the substrate;

[0058]FIG. 26A is a diagram showing a burr-removing member in the shapeof a cord, which is fed from a roll and wound onto another roll;

[0059]FIG. 26B is a diagram illustrating a burr-removing member in theshape of a cord (or belt) placed horizontal to the principal surface ofthe substrate;

[0060]FIG. 27 is a diagram showing an air knife as means for removingburrs;

[0061]FIGS. 28A and 28B are diagrams illustrating a burr-removing memberin the shape of a circular plate placed adjacent to the substrate;

[0062]FIGS. 28C and 28D are diagrams illustrating a burr-removing memberin the shape of a circular plate and a resin-removing device adjacentthereto;

[0063]FIG. 29 is a diagram showing a configuration of an apparatus forcarrying out a method of manufacturing the optical information recordingmedium, in which the process of supplying, applying and curing the resinare independently performed in the respective places, resulting insuppressing the generation of burrs, and

[0064]FIGS. 30A to 30C are diagram s each showing a structure forcorrecting the asymmetry of the optical information recording medium.

BEST MODE FOR CARRYING OUT THE INVENTION

[0065] Referring to the Drawings attached hereto, a method ofmanufacturing the optical information recording medium according to theinvention is described in detail below.

[0066] First Embodiment

[0067]FIG. 1 is a diagram illustrating the timing of the radiationirradiation in a method of manufacturing the optical informationrecording medium according to the present invention. Referring to thedrawing, the process of this embodiment includes the steps of supplyingor dropping a radiation cure type resin onto a substrate; spreading(applying) the radiation cure type resin by spinning; and then curingthe resin by irradiating radiation, when an optically transparent layeris formed from the resin on the substrate by spin coating. In theprocess, the rotation of the substrate is accelerated before theradiation is applied, and the radiation is irradiated to cure theradiation cure type resin during the acceleration. Such a process canproduce a uniform optically transparent layer. Such a process formanufacturing the optical information recording medium is described indetail below.

[0068]FIG. 2 shows a configuration of a manufacturing apparatus forcarrying out the inventive method of the optical information recordingmedium according to the invention. The manufacturing apparatus includesa rotary table 106 which mounts a substrate 101 of the opticalinformation recording medium and rotates or spins the substrate 101 at apredetermined speed, a motor 131 for rotating or spinning the rotarytable 106, a control circuit 132 for controlling the number ofrevolutions of the motor 131, a nozzle 113 for supplying or dropping theradiation cure type resin for an optically transparent layer onto thesubstrate 101, and a lamp 135 for irradiating radiation so that theradiation cure type resin can be cured to form the optically transparentlayer. The manufacturing method of optical information recording mediumby such an apparatus is described below.

[0069] The substrate 101 having a signal recording layer 102, athickness of 1.1 mm, a diameter of 120 mm, and a central hole 105 with adiameter of 15 mm, as shown in FIG. 3A, is placed on the rotary table106, and the central hole 105 is blocked with a cap 107, as shown inFIG. 3B. The cap 107 is made of metal and has a sealing 105 made of aTeflon® material at a portion to be in contact with the substrate 101.

[0070] While the substrate 101 is at rest or rotated at a low speed of120 rpm or lower, a radiation cure type resin 104 is started beingsupplied onto substantially the center of the cap 107 from a nozzle 113.The radiation cure type resin 104 has a viscosity of about 500 mPa·s atroom temperature, and the supplying rate is about 1 cm³/s. The viscosityof the radiation cure type resin and the supplying rate are preferablychanged depending on the thickness of the optically transparent layer tobe formed. In the optical disk for use with an NA of 0.85 and a laserbeam with a wavelength of 405 nm, the optically transparent layer shouldbe so formed that variations in its thickness is within about ±2% perabout 100 μm thickness and preferably controlled within about ±1%.

[0071] If the radiation cure type resin is supplied as near as possibleto the center, the thickness of the optically transparent layer formedon the signal recording layer 102 can easily become uniform from theinner radius to the outer radius. In this embodiment, the central holeis blocked with the cap 107, and the radiation cure type resin issupplied onto the cap 107, so that the effect can be maximal.

[0072] When the cap 107 used has a conical shape as shown in FIG. 3B,the resin 104 supplied from the cap 107 onto the signal recording layer102 can be uniform in the circumferential direction, so that thevariations can also be small in the radial direction.

[0073] Referring to FIG. 3C, while the radiation cure type resin 104 issupplied, the substrate 101 is rotated at about 350 rpm about threeseconds after the start of the supplying according to the time chart asshown in FIG. 4A, so that the radiation cure type resin 104 is appliedonto the signal recording layer and made uniform. It is noted that thenumber of revolutions in such an application step is called “the numberof application revolutions.” The number of application revolutions ispreferably changed depending on the thickness or the variations inthickness of the optically transparent layer to be formed.

[0074] In the process of the supplying, the radiation cure type resin104 can penetrate into a very small gap between the cap 107 and thesubstrate 101. The sealing 105 provided in the cap 107 can prevent suchpenetration.

[0075] In addition, the effect of preventing the resin penetration canbe enhanced by providing a mechanism of pulling the cap 107 downward (inthe direction to the table 106). As shown in FIG. 5, for example, such amechanism may include a suction hole 15 for pulling the cap 107 downwardby vacuum at the center of the rotary table 106. Alternatively, as shownin FIGS. 6A to 6C, such a mechanism may include a magnet 12 embedded inthe cap 107 and/or the rotary table 106. When the magnet 12 is embeddedin one of the cap 107 and the rotary table 106, a part or whole of theother is made of a metallic material.

[0076] Referring to FIG. 4A again, the supplying of the radiation curetype resin is stopped about 10 seconds after the start of the 350 rpmrotation. The supplying may be stopped rapidly or the amount of thesupplying may be gradually decreased. If the supplying is maintained fora while during the rotation, the feed of the radiation cure type resincan be balanced with the amount of the resin dissipated by spreading, sothat uniform application of the radiation cure type resin can be easy.

[0077] In such a balanced state, however, the thickness at the innerradius tends to be slightly greater than that at the outer radius. Afterthe stop of the supplying of the radiation cure type resin 104,therefore, the spreading (application) of the resin 104 is continued forabout 15 seconds while the substrate 101 is held rotated at a constantspeed. The rotation of the substrate 101 is then accelerated at about100 rpm/s. Referring to FIG. 7, when the number of revolutions of thesubstrate 101 reaches about 600 rpm during the acceleration, radiation110 is irradiated to cure the radiation cure type resin while thesubstrate 101 is accelerated. By such a process, the opticallytransparent layer can be formed uniformly up to the vicinity of theouter end of the substrate 101. After the radiation cure type resin 104is cured, the rotation of the substrate 101 is stopped.

[0078] If the curing is carried out after the rotation of the substrate101 is stopped, the optically transparent layer 104 can have a verylarge thickness at the outer end as shown in FIG. 8A. If the curing iscarried out at a constant rotation speed, the resin can be extremelythin at a region near the outer end as shown in FIG. 8B. If the curingis carried out in the process of decreasing the number of revolutions ofthe substrate 101, the optically transparent layer 104 can be formed tohave thin and thick portions at the same time as shown in FIG. 8C. Inthis embodiment, however, the curing is carried out during theacceleration of revolutions of the substrate 101 as described above, sothat the thickness can be made uniform up to the vicinity of theoutermost end. The acceleration is preferably changed depending on theviscosity of the radiation cure type resin 104, because a too highacceleration can increase variations in thickness.

[0079] When the radiation cure type resin 104 is applied onto thesubstrate 101 by spinning, a part of the outer peripheral portion cannot be coated with the resin 104 depending on the wettability of thesignal recording layer 102 with the resin 104. In order to solve thisproblem, the time chart as shown in FIG. 4B may be used. According tothe time chart, the number of application revolutions may be transientlymade higher (for example, 1000 rpm) than the usual number (for example,about 350 rpm) in the step of resin application before the acceleration,and the high speed rotation may be maintained for a predetermined period(for example, about one second) when the radiation cure type resin 104is applied over the surface of the signal recording layer 102. Thenumber of application revolutions may then be returned to the original(for example, about 350 rpm).

[0080] Alternatively, the curing of the resin may be performed after theacceleration (not during the acceleration). Specifically, the number ofrevolutions of the substrate 101 may be made higher than the number ofapplication revolutions and then held at the higher number for a certaintime period, and the curing may be performed immediately after suchholding. As shown in FIG. 9, for example, the number of revolutions maybe raised higher (for example, 1000 rpm) than the number of applicationrevolutions, and the curing may be performed within a certain timeperiod after the stop of the acceleration, for example, within about twoseconds after the raise in the number of revolutions. Such a process canalso bring about an effect substantially equivalent to that achievedduring the acceleration.

[0081] The curing of the radiation cure type resin is preferablycompleted in a time as short as possible. In this embodiment, used is anapparatus that can apply pulses with high intensity from a xenon lightsource. If the curing takes much time, a difference in degree ofspreading to the outer end can be made between the cured and uncuredportions of the resin and the optically transparent layer can fail tohave a uniform thickness, because the resin is cured while the substrateis rotated. Therefore, radiation is preferably irradiated with suchintensity that the curing can be completed within one second.

[0082] In the process of irradiating the radiation, the radiation ispreferably not irradiated to the outer end of the substrate or thedetached (spun-off) radiation cure type resin, so that the spun-offresin can be recovered and subjected to a process such as filtration forreuse. In addition, the nozzle 113 is preferably moved away from theradiation so as not to be irradiated during the radiation irradiation.

[0083] If the radiation is irradiated or applied to the outer end faceof the substrate 101, burrs can be generated as shown in FIGS. 10A and10B. It is preferred that the burrs be removed, because they can cause aproblem with appearance or mechanical characteristics such as devianceof center of mass. For example, as shown in FIG. 10C, the burrs may becut off by iiradiation of a laser beam 112, or as shown in FIG. 10D bymeans of a sharp metal or a cutting tool such as a cutter 113, or theburrs may be melted and removed by heat treatment. In addition, thecuring at the outer end face may be inhibited by using a radiation curetype resin that is hard to cure in an atmosphere containing an excessamount of oxygen and placing the outer end portion in such an oxygenexcess atmosphere in the process of radiation irradiation.

[0084] Some types of radiation cure type resin can cause problems suchas low hardness after the curing and easiness of receiving damage, highcoefficient of friction and easiness of receiving damage, or easiness ofreceiving dusts. Against such problems, a hard coat 114 may be providedon the resin as shown in FIG. 11A.

[0085] Referring to FIG. 11B, the cap 107 is removed after the radiationcuring. If the hard coat is provided, the cap 107 may be removed beforeor after the hard coating.

[0086] In this embodiment, a rewritable recording/reproducing typeoptical disk is provided as an example. Alternatively, may be provided awrite-once type optical disk or a read-only type disk having areflecting layer mainly composed of Al or Ag. A multilayer optical diskhaving two or more signal recording layers may also be provided.

[0087]FIG. 12 shows a radius-dependency of the thickness of theoptically transparent layer in the optical information recording mediumaccording to the embodiment of the invention. According to the method ofthe present invention, even distribution of thickness has been achievedin such a manner that variations in thickness defined by the peak topeak value are controlled to 2 μm or less per 100 μm thickness entirelyranging from the inner radius to the outer radius. The resultinghigh-density optical recording medium used with a blue laser has broughtabout a significant effect, that is, good reproduction characteristicsfrom the innermost to the outermost (at a radius of 58.5 mm).

[0088] The above-described embodiment is not intended to limit the scopeof the invention, and any other embodiments may also be provided basedon the technical idea for the invention.

[0089] Second Embodiment

[0090]FIGS. 13A to 13C shows a nozzle for supplying the radiation curetype resin 104, which is used in this embodiment. FIG. 13A is a view ofthe bottom of the nozzle, FIG. 13B is a sectional view thereof, and FIG.13C is a perspective view thereof. In this embodiment, the radiationcure type resin 104 is supplied using a nozzle 201 that has a pluralityof openings 202 arranged at substantially the same radius as shown inFIGS. 13A to 13C. In the nozzle 201, eighteen openings 202 are providedat a radius of r (25 mm).

[0091] Similarly to First Embodiment, the substrate 101 is mounted onthe rotary table 106. The nozzle 201 as shown in FIGS. 13A to 13C isused to supply the radiation cure type resin 104 onto portions locatedat substantially the same radius on the substrate 101. Such a nozzle 201avoids the necessity for using the cap 107 of First Embodiment or thelike. If the radiation cure type resin is supplied onto the cap 107 asin First Embodiment, problems of detachment and reuse of the cap 107 canappear after the curing of the resin. In contrast, such processes areunnecessary for this embodiment. For the purpose of making the thicknessof the optically transparent layer uniform from the inner radius to theouter radius, the openings 202 of the nozzle 201 is preferably as nearas possible to the central hole 105 of the substrate 101.

[0092]FIGS. 14A to 14C show another example of the nozzle. FIG. 14A is aview of the bottom of the nozzle, FIG. 14B is a sectional view thereof,and FIG. 14C is a perspective view thereof. Referring to the drawings,the nozzle 203 has a ring-shaped opening 204 for ejecting the resin. Thenozzle 203 can bring about a similar effect.

[0093] If the radiation cure type resin 104 has such a viscosity or thelike that the central hole of the substrate can be stained with theresin 104, the nozzle of this embodiment may be used in combination withthe cap 107 of First Embodiment. Alternatively, air may be blown fromthe side of the central hole 105 of the substrate 101 to the outerradius side to prevent the radiation cure type resin 104 frompenetrating.

[0094] The steps of First Embodiment are used after the step ofsupplying the resin from the nozzle.

[0095] Third Embodiment

[0096] In First and Second Embodiments, the application of the radiationcure type resin 104 and the curing by the radiation irradiation areperformed in the same place. In such a process, however, the spun-offradiation cure type resin can be cured while adhering to the units suchas the rotary table 106 and cause some trouble with the operation of therotary table 106. If some mechanism is provided to prevent such trouble,the apparatus can be complicated.

[0097] In this embodiment, therefore, the supplying/application of theradiation cure type resin 104 and the curing by the radiationirradiation are independently performed in different places.

[0098] For example, at the time when application of the radiation curetype resin is made to some extent, the substrate 101 is stopped fromrotating and then transferred to another place for radiationirradiation. At the another place, radiation is irradiated while therotation of the substrate is accelerated, for example, at 100 rpm/s.FIG. 15 shows a time chart in such a case. The process of applying andcuring the radiation cure type resin 104 in different places can reducethe amount of the spun-off and cured resin. It can also be easy toprovide a mechanism for reducing the amount of the spun-off radiationcure type resin.

[0099]FIG. 16 shows a configuration of an apparatus for carrying out theabove process. As shown in the drawing, the apparatus includes a rotarytable 106 made of metal and transfer means 137 having a magnet 138 atits tip. The table 106 and the substrate 101 are lifted together by thetransfer means 137 and separated from the motor 131 which is placedwhere the resin is supplied and applied, and then transported to anotherplace for resin curing and placed on a motor 131 b in the another place.Such a configuration can raise the recycle ratio of the radiation curetype rein, so that the manufacturing cost can be reduced. In addition,each step is independently carried out, and therefore, the manufacturingapparatus can easily be built.

[0100] As described above, the substrate 101 may be once stopped fromrotating and then rotated again. Even through such a process, theoptically transparent layer can be formed uniformly up to the outer endby the process of irradiating radiation to cure the resin during theacceleration, similarly to First Embodiment. The optically transparentlayer can uniformly be formed over the entire surface of the signalrecording layer.

[0101] In the example as shown in FIG. 16, the table 106 and thesubstrate 101 mounted thereon are transferred to another place.Alternatively, only the substrate 101 may be moved to another place. Forexample, such transfer can be made using a three-claw pin 139 as shownin FIG. 17 in place of the above magnet 138. The substrate 101 can beheld at a center portion thereof by the pin 139 and lifted.

[0102] Fourth Embodiment

[0103] The description below is about the fourth embodiment of theinventive method of manufacturing the optical information recordingmedium.

[0104] In First Embodiment, the cap 107 is detached after the radiationcure type resin 104 is cured. However, the following problems can becaused in this case. The radiation-cured resin on the signal recordinglayer 102 can be cracked in the step of detaching the cap 107, dependingon the hardness and the thickness of the radiation-cured resin. Theportion from which the cap 107 is detached can have burrs or the like,which can affect the holding of the optical information recording mediumat the time of recording or reproducing.

[0105] In this embodiment, therefore, the cap 107 is detached before theradiation irradiation, and then radiation is applied to cure theradiation cure type resin on the substrate 101. The cap 107 can bereused if it is subjected to a cleaning process. The cap 107 ispreferably removed so that the cap 107 is not irradiated by theradiation.

[0106] Thus, the cap 107 can be reused any number of times, and auniform optically transparent layer can be formed with no adverse effecton the resin 104 on the signal recording layer 102.

[0107] According to the method of manufacturing the optical informationrecording medium in First to Fourth Embodiments, the opticallytransparent layer can be formed uniformly over the signal region of thesubstrate, though such a uniform optically transparent layer has beendifficult to form by conventional spin coating methods. Specifically,the problem of a projection at the outer end of the opticallytransparent layer and the problem of a thinner part at the inner radiuscan be solved, so that the medium can easily be produced.

[0108] Fifth Embodiment

[0109] In this embodiment, described is a method of manufacturing theoptical information recording medium which can prevent burrs from beinggenerated at the outer end of the optical information recording medium.FIG. 18 is a diagram (a section viewed from a side) showing a member forremoving burrs, which is placed at the outer end of the opticalinformation recording medium. Referring to the drawing, a member 103 forremoving the resin protruding from the outer end of the opticalinformation recording medium (a removing member) is provided at theouter end of the optical information recording medium. Burrs generatedat the outer end of the optical information recording medium can beremoved using the member 103.

[0110] One example of a method of manufacturing the optical informationrecording medium according to the invention is shown below. Thesubstrate 101 having the signal recording layer 102, a thickness of 1.1mm, a diameter of 120 mm, and a central hole 105 with a diameter of 15mm, as shown in FIG. 19A, is placed on the rotary table 106 with thecentral hole 105 blocked by the cap 107, as shown in FIG. 19B. The cap107 is made of metal and has a conical outer shape. The inside of thecap 107 has a doughnut-shaped hollow structure so that only theoutermost of the cap 107 is in line-contact with the substrate 101. Thecap 107 may be coated with Teflon® so that adhesion of the radiationcure type resin can be prevented.

[0111] While the substrate 101 is stopped or rotated at a low speed of120 rpm or less, the radiation cure type resin 104 is added suppliedonto substantially the center of the cap 107 from the nozzle 113. Theradiation cure type resin 104 has a viscosity of about 500 mPa·s at roomtemperature and is supplied at a rate of about 1 cm³/s. The viscosity ofthe radiation cure type resin 104 and the supplying rate are eachpreferably changed depending on the thickness of the opticallytransparent layer to be formed.

[0112] If the radiation cure type resin 104 is supplied as near aspossible to the center, the thickness of the optically transparent layerformed on the signal recording layer 102 can easily become uniformranging from the inner radius to the outer radius. In this embodiment,the central hole 105 is blocked with the cap 107, and the radiation curetype resin 104 is supplied onto the cap 107, so that the effect can bemaximal. The cap used here has a diameter of 23 mm.

[0113] As shown in FIG. 19B, the cap 107 has such a doughnut-shapedhollow structure that only its outermost is in line-contact with thesubstrate 101. The cap 107 having such a structure can prevent theradiation cure type resin from penetrating to the contact surfacebetween the cap 107 and the substrate 101 due to capillary action. Suchan effect can be enhanced by providing a mechanism of pulling the cap107 downward, specifically by providing, at the center of the rotarytable 106, a suction hole for pulling the center of the cap 107 downwardas shown in FIG. 5. Alternatively, the cap may have a structure as shownin each of FIGS. 6A to 6C.

[0114] For example, a nozzle as shown in FIGS. 13A to 13C or FIGS. 14Ato 14C may be used to supply the radiation cure type resin 104 in acircular form onto the vicinity of the central hole of the substrate,and then the resin may be spread, so that a uniform layer can be formed.In such a case, there is no need to use the cap 107.

[0115] Referring to FIG. 19C, while the radiation cure type resin 104 issupplied, the substrate 101 is rotated at about 350 rpm about threeseconds after the start of the supplying, so that the radiation curetype resin 104 is applied onto the signal recording layer and made even.

[0116] The supplying of the radiation cure type resin 104 is stoppedabout 10 seconds after the start of the 350 rpm rotation. The supplyingmay be stopped rapidly or the supplying amount may be graduallydecreased. If the supplying is maintained for a while during therotation, the feed of the radiation cure type resin 104 can be balancedwith the amount of the resin dissipated by spreading, so that uniformapplication of the radiation cure type resin 104 can be easy.

[0117] In such a balanced state, however, the thickness at the innerradius tends to be slightly greater than that at the outer radius. Afterthe stop of the supplying of the radiation cure type resin 104,therefore, the spreading of the resin 104 is continued for about 15seconds while the substrate 101 is held rotated. The rotation of thesubstrate is then accelerated at about 100 rpm/s. Referring to FIG. 7,when the number of revolutions of the substrate reaches about 600 rpm,radiation 110 is irradiated to cure the radiation cure type resin 104while the substrate is accelerated, so that the optically transparentlayer 115 is formed. By such a process, the optically transparent layercan be formed uniformly up to the vicinity of the outer end of thesubstrate. After the radiation cure type resin is cured, the rotation ofthe substrate is stopped. The time chart for the above entire process isas shown in FIG. 4A.

[0118] Particularly in this embodiment, the member 103 is brought intocontact with the outer end of the substrate 101 while the rotary table106 is rotated, in the process of curing the radiation cure type resin104 (see FIG. 18). In such a process, the radiation cure type resin 104is spread to the member 103 and scraped off, so that a uniform opticallytransparent layer can be formed without generating burrs at the outerend of the substrate 101. In such a process, the member 103 may beplaced so as to be substantially in contact with the substrate 101before the radiation cure type resin 104 is supplied. Alternatively, themember 103 may be placed so as to be substantially in contact with thesubstrate 101 after the radiation cure type resin 104 is supplied andimmediately before the radiation 110 is irradiated.

[0119] In this embodiment, the member 103 is made of metal.Alternatively, the member 103 may be made of a resin material such aspolyurethane and polyacetal, for the purpose of preventing thepossibility of damage to the substrate 101. The material soluble in theradiation cure type resin 104 is preferably avoided.

[0120] If the member 103 is not used in the process of irradiatingradiation to cure the radiation cure type resin on the substrate beingrotated, the burrs 111 can be generated as shown in FIGS. 20A and 20B tocause a problem with appearance and a problem with mechanicalcharacteristics such as deviance of center of mass.

[0121] The member 103 placed at the outer end scrapes the unnecessaryradiation cure type resin, which would otherwise cause burrs at theouter end. Semi-cured burrs generated after the radiation irradiationare also scraped and removed by the member 103. The burrs are eliminatedby the member 103 mainly through these two processes.

[0122] Preferably, the level of the top face of the member 103 issubstantially equal to or higher than that of the surface of thesubstrate 101 having the signal recording layer 102. If the level is toolow, burrs are generated as shown in FIGS. 20A and 20B similarly to thecase where the member 103 is not provided.

[0123] If the top face of the member 103 is placed higher than thesignal recording layer 102, a burr 111 projecting upward as shown inFIG. 20C can be generated when the member 103 is located so as to be incontact with the substrate 101. A burr 111 can be prevented by keeping alittle distance (about 1 mm in this embodiment) between the substrateand the member. If the rotation of the substrate 101 is notcenter-symmetrical (with eccentricity), it will be difficult to maintaina constant distance between the substrate 101 and the member 103. Inorder to keep a certain distance between the substrate and the member, aprojection is preferably provided at the rotation center of the surfaceof the rotary table 106 so as to fit into the central hole of thesubstrate 101. Such a structure can easily reduce the eccentricity to100 μm or less.

[0124] In the case that the burrs are prevented by the member 103 whichis in contact with the substrate 101 and whose top level issubstantially equal to that of the surface of the substrate 101 havingthe signal recording layer 102, the member may be pressed to thesubstrate by applying a certain pressure. If the pressure is too high,it can affect the rotation of the substrate 101. Therefore, the pressureis preferably as low as possible unless the contact is broken. Forexample, the pressure is preferably from 10⁻⁴ to 1 N/m², particularlypreferably from 10⁻⁴ to 10⁻² N/m².

[0125] The top face of the member 103 may not be parallel to the surfaceof the substrate 101 having the signal recording layer 102. For example,as shown in FIG. 21A or 21B, a member 123 or 124 may be provided whosetop face is inclined toward the outer side, or as shown in FIG. 21C(viewed from the outer side to the center of the substrate 101), amember 125 may have such a shape that the top face is inclined towardthe direction of rotation. The angle and the shape of the burr may varydepending on the viscosity of the radiation cure type resin 104 and thenumber of revolutions. Therefore, it is preferred that an optimal memberis selected depending on such situations.

[0126] Referring to FIG. 22A, the member 103 may be a circular cylinderso as to have the substrate 101 inside. Alternatively, as shown in FIG.22B or 22C, the member 103 may have a rectangular shape. The member 103may also have a shape along the periphery of the substrate 101 (forexample, a member 122 in an arc shape as shown in FIG. 22D). Although inthis embodiment, the member is placed at a single position, such amember may be placed at different positions, respectively.

[0127] It is preferred that the member or the spun-off radiation curetype resin 104 is not irradiated in the process of applying radiation110. Thus, the spun-off radiation cure type resin 104 can be recoveredand subjected to a process such as filtration, so that the resin 104 canbe reused. Further it can prevent deterioration of peripheryburr-removing effect which is caused by the radiation cure type resin104 adhering to the member 103 and curing to deform the member 103.

[0128] Thus, a shielding plate 11 as shown in FIG. 23B is preferablyused so that the radiation cure type resin 104 can be cured only on thesubstrate 101 as shown in FIG. 23A. In this embodiment, the shieldingplate 151 which has a hole 151 b with a radius of r substantially equalto that of the substrate 101, is placed as shown in FIG. 7B so thatradiation 110 is irradiated only to the substrate 101.

[0129] A radiation cure type resin 104 that is difficult to cure in anatmosphere containing an excess amount of oxygen may also be used. Ifsuch a resin is used and the member 103 is placed in such an oxygenexcess atmosphere in the process of applying radiation, the resin 104adhering to the member 103 can effectively be prevented from beingcured.

[0130] Some types of radiation cure type resin can cause problems suchas I easiness of receiving damage by low hardness after the curing orhigh coefficient of friction, or easiness of receiving dusts. Againstsuch problems, a protective layer 112 may be formed on the opticallytransparent layer 115 as shown in FIG. 24A. In this embodiment, theprotective layer 112 is formed with a thickness of about 3 μm by aconventional spin coating method. Alternatively, the protective layer112 may be formed by the inventive method for forming the opticallytransparent layer.

[0131] In addition, the material for the protective layer may have thefunction of preventing the optically transparent layer from absorbingmoisture or the like. Such a protective layer can prevent the opticallytransparent layer from suffering moisture damage or from expanding bymoisture absorption. For example, a dielectric film or the like formedwith a thickness of about 3 nm to about 50 nm by sputtering or the likecan bring about such an effect.

[0132] The protective layer may be composed of different layers ofdifferent materials so as to have the different functions as describedabove.

[0133] The process of this embodiment includes the steps of: masking thecentral hole 105 with the cap 107 when the optically transparent layeris formed; and removing the cap 107 after the optically transparentlayer is formed. If the protective 112 layer is formed, however, the capmay be removed at any time before or after the protective layer isformed. Referring to FIG. 24B, the cap 107 can easily be detached bysucking a suck portion 141 and pressing a push portion 142 upward.Referring to FIG. 24B, the optically transparent layer forms a step 130at the inner radius region of the substrate 101 after the cap 107 isremoved. Therefore, the diameter of the cap 107 is preferably soselected that such a step is not located in the region (the clampregion) that is supported in the process of reading or writing into theoptical disk.

[0134] After detached, the cap 107 may be subjected to a process such ascleaning for removing the adhering radiation cure type resin and thenreused.

[0135] According to this embodiment, the optically transparent layer canbe formed with a thickness of about 100 μm, and variations in thicknessof the optically transparent layer on the signal recording layer 102 canbe controlled to 3 μm or less. Thus, even under the conditions of an NAof about 0.85 and a laser beam wavelength of about 400 nm, recording andreproducing can be made in good quality, and a tilt margin equivalent tothat for DVD can be ensured.

[0136] The signal recording layer 102 may be any of a rewritable type, awrite-once type, and a read-only type having a reflecting layer mainlycomposed of Al or Ag. As shown in FIG. 24C, a multilayer optical diskhaving a plurality (two or more) of signal recording layers may also beprovided. Referring to FIG. 24C, a separation layer 119 is provided toseparate two signal recording layers 102 and 118. In terms ofrecording/reproducing characteristics, the separation layer 119preferably has a thickness of about 30 μm.

[0137] Sixth Embodiment

[0138] Referring to FIG. 25A, in this embodiment, a cord-shaped member401 is used for removing the burrs generated at the outer end of thesubstrate 101. The cord-shaped member 401 is provided in the verticaldirection so as to be in contact with the end face. This member canbring about the same effect as the member 103 in First Embodiment. Thecord-shaped member 401 is kept under a certain tension so as to be incontact with the outer end of the substrate 101.

[0139] For example, as shown in FIG. 25B, the cord-shaped member 401 isformed into an annular ring shape and rotated while being in contactwith the outer end of the substrate 101. The radiation cure type resin104 adhering to the member 401 is removed by a removing device 215. Sucha system can recover the resin and provide increased productionefficiency. Referring to FIG. 26A, the cord 401 may be supplied from aroll 217 and recovered onto a roll 217 together with the radiation curetype resin 104 attached to the cord. Such a system can fully recover theresin, even when the removing device 215 does not have enoughperformance to remove the resin.

[0140] The cross section of the cord-shaped member 401 may be in anyshape, specifically in the shape of a circle, an ellipse, a rectangular,or the like. It is preferred that the material and the surface conditionfor the cord-shaped member 401 should be determined depending onfriction with the substrate and the degree of the effect of eliminatingburrs.

[0141] Similarly to Fifth Embodiment, the shielding plate may also beused for preventing the radiation cure type resin 104 attached to themember 401 from being cured, or the steps of spreading and curing theradiation curing resin may independently be carried out in differentplaces.

[0142] Seventh Embodiment

[0143] In this embodiment, a high pressure gas ejected from a certainoutlet (hereinafter referred to as “air knife”) is used for removingburrs in place of the member 103 provided at the outer end of thesubstrate 101. Referring to FIG. 27, an air knife 316 is ejected by highpressure from an air outlet 317 below the substrate 101 and applied tothe outer end, so that the same effect can be achieved as in FifthEmbodiment with the member 103.

[0144] In Fifth Embodiment, attention should be paid not to cure theradiation cure type resin 104 attached to the member 103. When the airknife 316 is used, there is no need to pay such attention, and thereforethe production efficiency can significantly be increased. The air knife316 is preferably ejected immediately before the radiation cure typeresin 104 is cured by radiation irradiation.

[0145] In the method as shown in FIG. 27, the air knife 316 is outputfrom the air outlet 317 below the substrate 101 toward the outer end ofthe substrate 101. Alternatively, the air knife 316 may be applied fromabove or in a slanting direction to the outer end of the substrate 101.The air knife 316 may be applied to one portion or different portions ofthe substrate 101. The air knife outlet 317 may have a doughnut-shapedoutlet opening with a radius substantially equal to that of thesubstrate 101. Such an air knife outlet 31 can apply the air knife 316to the entire periphery of the substrate 101 at the same time.

[0146] Eighth Embodiment

[0147] Referring to FIGS. 28A and 28B, in this embodiment, a member 402for removing burrs is in the shape of a circular plate and placed insuch a manner that the level of its top face is substantially equal toor slightly higher than that of the surface of the substrate 101 havingthe signal recording layer 102. The member 402 is adapted to be rotatedby the rotation of the substrate 101.

[0148] The member 402 is rotated by the rotation of the substrate 101 inthe reverse direction to the substrate 101 at substantially the sameperipheral speed. The rotated member 402 can more effectively remove theunnecessary radiation cure type resin 104 at the outer end of thesubstrate 101. The burrs can be prevented at the outer end even whenradiation is applied to cure the radiation cure type resin 104 on thesubstrate 101 being rotated. In this embodiment, the member 402 usessuch a mechanism that it is driven by the rotation of the substrate 101.Alternatively, a drive mechanism for rotating the member 402 may be soprovided that the member 402 can be rotated by independent drivingforce. In such a drive mechanism, when the member 402 rotates in thesame direction as the substrate 101 or linear speed of the outer end ofthe member 402 is different from that of the substrate 101, highfriction can be generated between the substrate 101 and the member 402,so that uniformity of the optically transparent layer can be degraded.Therefore, the member 402 and the substrate 101 are preferably rotatedin the reverse direction at substantially the same linear speed of theouter end.

[0149] During the rotation of the member 402, The radiation cure typeresin which adhere to the rotated member 402 can fly out to thesubstrate 101 again as a droplet. In such a case, the opticallytransparent layer can be formed with increased variations in thickness.Therefore, a device 415 for removing the radiation cure type resin ispreferably provided at the portion of the member 402 which is not incontact with the substrate 101.

[0150] In place of the above circular member 402, the cord orbelt-shaped member 401 as in the above embodiments may be provided asshown in FIG. 26B, wherein the member 401 is placed in the horizontaldirection with respect to the surface of the substrate 101 and rotatedso that the same effect can be achieved.

[0151] As in Fifth Embodiment, the member 402 may be in contact with thesubstrate 101 or separated from the substrate 101 with a little distance(for example, 1 mm). The easiness of generating burrs may vary dependingon the viscosity of the radiation cure type resin 104 or the number ofrevolutions. It is therefore preferred that an optimal distance betweenthe member 402 and the substrate 101 is determined depending on eachcondition.

[0152] Ninth Embodiment

[0153] In Fifth Embodiment, both the step of applying/spreading theradiation cure type resin and the step of curing the resin on thesubstrate being rotated are carried out in the same place. Duringradiation irradiation, the shielding plate or the like may be used toprevent the spun-off resin from being irradiated. Even in such a case,the spun-off resin can be cured little by little, if a slight leak ofthe radiation is accumulated. In such a case, the recovery and reuse ofthe radiation cure type resin can not be done well and thus the cost canbe high.

[0154] In each of Fifth to Eighth Embodiments, therefore, the processpreferably includes the steps of: applying and spreading the radiationcure type resin; then stopping the rotation of the substrate andtransferring the substrate to a different place; and curing the resin onthe substrate being rotated in the different place, as in ThirdEmbodiment.

[0155]FIG. 29 shows a configuration of an apparatus for such a process.The member 103 for preventing burrs at the outer end of the substrate101 may be provided only in the place where the radiation is irradiated.Since the two steps are carried out in separated places, the apparatuscan be simplified.

[0156] Tenth Embodiment

[0157] Referring to FIG. 30A, the optical information recording medium(disk) obtained in each of the above embodiments is an asymmetrical diskhaving the optically transparent layer 115 provided on one principalsurface of the substrate 101. It is known that the optically transparentlayer 115 produced by curing the radiation cure type resin can usuallyshrink at high temperature or undergo water absorption and expansion ordewatering and shrinkage depending on a change in atmospheric humidity.In the asymmetrically-structured disk, therefore, the tilt cansignificantly fluctuates with an increase in temperature or asignificant change in humidity, which can lead to degradation of recordor reproduction.

[0158] Referring to FIG. 30B, therefore, a layer (a balance layer) 501similar to the optically transparent layer is formed on the surface(back surface) opposite to the surface having the signal recording layer102, so that the asymmetry can be corrected. Such a structure cansignificantly reduce the change in tilt, which would otherwise be causedby a change in temperature or humidity. Referring to FIG. 30C, a signalrecording layer 502 may also be provided on the back surface to form adouble-sided recording/reproducing type disk, which is improved withrespect to symmetry.

[0159] For the purpose of achieving high symmetry in such a structure,the layers formed on both surfaces are preferably substantially equal inmaterial characteristics (such as characteristics on water absorptionexpansion or dewatering shrinkage (shrinkage characteristics) andthickness. If a different material is used to form the layer on the backsurface, it is preferred that the thickness of the layer on the backsurface should be changed based on the balance of a change in tilt. Theprotective layer 112 may also be formed on the back surface.

[0160] According to the manufacturing method of the optical informationrecording medium of the present invention, the optically transparentlayer can be formed uniformly over the signal region of the substrate,though such a uniform optically transparent layer has been difficult toform by conventional spin coating methods. The outer end of thesubstrate can also be free from burrs which would otherwise begenerated, by irradiating radiation to cure the radiation cure typeresin on the substrate being rotated.

[0161] It will be understood that any combinations of theabove-described embodiments, examples or technical ideas are availableto those skilled in the art. Although the invention has been describedin connection with specific embodiments, many other modifications,variations and applications are apparent to those skilled in the art.Therefore, the scope of the invention is not limited by the specificdisclosure as provided herein but should be limited only by the appendedclaims.

1. A method of manufacturing an optical information recording mediumthat comprises a substrate having a signal recording layer formed on oneprincipal surface thereof; and an optically transparent layer formed onthe signal recording layer and made from a radiation cure type resin,the method comprising: when the optically transparent layer is formed,supplying the radiation cure type resin onto the substrate; applying theradiation cure type resin over the substrate by spinning the substrateat a predetermined number of application revolutions in a spin coatingmethod; increasing the number of revolutions of the substrate after theapplication of the resin; and irradiating radiation to cure theradiation cure type resin while the number of revolutions of thesubstrate is increased.
 2. A method of manufacturing an opticalinformation recording medium that comprises a substrate having a signalrecording layer formed on one principal surface thereof; and anoptically transparent layer formed on the signal recording layer andmade from a radiation cure type resin, the method comprising: when theoptically transparent layer is formed, supplying the radiation cure typeresin onto the substrate; applying the radiation cure type resin overthe substrate by spinning the substrate at a predetermined number ofapplication revolutions in a spin coating method; increasing the numberof revolutions of the substrate to a predetermined number of revolutionsthat is greater than the predetermined number of application revolutionsafter the application of the resin; maintaining the predetermined numberof revolutions after the number of revolutions reaches the predeterminednumber of revolutions; and irradiating radiation to cure the radiationcure type resin within a predetermined period after the number ofrevolutions reaches the predetermined number of revolutions.
 3. Themethod according to claim 1 or 2, further including, after the supplyingthe radiation cure type resin and before the increasing the number ofrevolutions, transiently spreading the radiation cure type resin at asecond number of application revolutions that is greater than the numberof application revolutions.
 4. The method according to claim 1 or 2,wherein the applying the radiation cure type resin at the number ofrevolutions and the irradiating the radiation to cure the radiation curetype resin are independently carried out in different locations.
 5. Themethod according to claim 1 or 2, wherein the radiation cure type resinis cured by the radiation irradiation within one second.
 6. The methodaccording to claim 1 or 2, further, comprising: starting supplying theradiation cure type resin while the substrate is spinning at a speedlower than a predetermined speed; starting applying the radiation curetype resin over the substrate by spinning the substrate at a speedhigher than the lower speed; and afterward stopping the supplying theradiation cure type resin, and then stopping the applying the radiationcure type resin.
 7. A method of manufacturing an optical informationrecording medium that comprises a substrate having a signal recordinglayer formed on one principal surface thereof; and an opticallytransparent layer formed on the signal recording layer and made from aradiation cure type resin, the method comprising: when the opticallytransparent layer is formed, supplying the radiation cure type resinonto different portions located at substantially the same radius insidethe region where the signal recording layer is formed; and applying thesupplied radiation cure type resin over the substrate by spreading thesupplied radiation cure type resin.
 8. The method according to claim 7,wherein a nozzle having a plurality of openings at substantially thesame radius is used to supply the radiation cure type resin.
 9. Themethod according to claim 1 or 2, wherein, when the opticallytransparent layer is formed, supplied is the radiation cure type resinin the shape of a ring at substantially the same radius inside theregion where the signal recording layer is formed; and the suppliedradiation cure type resin is applied over the substrate by spreading thesupplied radiation cure type resin.
 10. The method according to claim 9,wherein a nozzle having a ring-shaped opening is used to supply theradiation cure type resin.
 11. The method according to claim 7 or 9,wherein the radiation cure type resin is supplied while the substrate isspinning.
 12. The method according to claim 1, 2 or 7, wherein thesubstrate has a central hole, and the central hole is blocked when theradiation cure type resin is supplied.
 13. The method according to claim7 or 9, wherein an air or gas flowing from the central hole side to theouter radius side of the substrate is produced for a predeterminedperiod while the radiation cure type resin is supplied.
 14. The methodaccording to claim 1 or 2, wherein the substrate has a central hole, andthe method further comprises blocking the central hole with a memberhaving a sealing to prevent the radiation cure type resin from leakinginto at a portion adjacent to the substrate, during the supplying theradiation cure type resin.
 15. The method according to claim 14, whereinthe member for blocking the central hole has a conical shape.
 16. Themethod according to claim 14, wherein the substrate is mounted on arotary table and rotated, and means for pulling downward the member forblocking the central hole on the substrate is provided to bring themember for blocking the central hole into close contact with thesubstrate.
 17. A method of manufacturing an optical informationrecording medium that comprises a substrate having a signal recordinglayer formed on one principal surface thereof; and an opticallytransparent layer formed on the signal recording layer and made from aradiation cure type resin, the method comprising irradiating radiationto cure the radiation cure type resin while spinning the substrate,wherein an end face portion of the substrate is placed in an atmospherecontaining an excess amount of oxygen when the radiation is irradiated.18. The method according to claim 1 or 2, further comprising removing aburr from an outer end face portion of the substrate after the radiationcure type resin is cured.
 19. The method according to claim 18, whereinthe burr at the outer end of the substrate is removed by laser beamirradation.
 20. The method according to claim 18, wherein the burr atthe outer end of the substrate is removed using a sharp metal.
 21. Themethod according to claim 18, wherein the irradiating the radiation andthe removing the burr are independently carried out in differentlocations.
 22. The method according to claim 1, 2, 7 or 17, wherein theoptically transparent layer has a thickness of about 0.1 mm.
 23. Themethod according to claim 1, 2, 7 or 17, further comprising forming aprotective layer over the optically transparent layer.
 24. A method ofmanufacturing an optical information recording medium that comprises asubstrate having a signal recording layer formed on one principalsurface thereof; and an optically transparent layer formed on the signalrecording layer and made from a radiation cure type resin, the methodcomprising: applying the radiation cure type resin onto the signalrecording layer in a spin coating method; increasing the number ofrevolutions of the substrate after the applying; and irradiatingradiation to cure the radiation cure type resin while increasing thenumber of revolutions, thereby forming the optically transparent layer,wherein a predetermined member is placed so as to be substantially incontact with the outer end of the principal surface while the substrateis spinning.
 25. The method according to claim 24, wherein thepredetermined member is in the shape of a cord.
 26. The method accordingto claim 24, wherein the predetermined member has a top face whose levelis substantially equal to that of the principal surface of thesubstrate.
 27. The method according to claim 24, wherein a section ofthe predetermined member that is parallel to the principal surface ofthe substrate is circular.
 28. The method according to claim 24, whereinthe predetermined member is rotatable.
 29. The method according to claim28, wherein the predetermined member is rotated by the rotation force ofthe substrate.
 30. The method according to claim 28, wherein thepredetermined member is rotated by a power different from a power forrotating the substrate.
 31. The method according to claim 28, whereinthe predetermined member is rotated in the reverse direction to that ofthe substrate.
 32. The method according to claim 28, wherein thepredetermined member is rotated at a linear speed substantially equal tothat of the substrate at an outer end.
 33. The method according to claim24, wherein the radiation cure type resin adhering to the predeterminedmember is removed using another member different from the predeterminedmember.
 34. The method according to claim 24, wherein the distancebetween the predetermined member and the substrate is at most 1 mm. 35.The method according to claim 24, wherein the predetermined member isequipped with a mechanism for constantly bringing the member intocontact with the substrate.
 36. A method of manufacturing an opticalinformation recording medium that comprises a substrate having a signalrecording layer formed on one principal surface thereof; and anoptically transparent layer formed on the signal recording layer andmade from a radiation cure type resin, the method comprising: applyingthe radiation cure type resin on the signal recording layer in a spincoating method; and irradiating radiation only to the substrate to curethe radiation cure type resin while spinning the substrate, therebyforming the optically transparent layer, wherein a high pressure gas jetis applied to at least one portion of the outer end of the principalsurface while the substrate is spinning.
 37. (Cancelled).
 38. The methodaccording to claim 36 wherein a shielding plate having a holesubstantially equal to the substrate in shape is used when the radiationis irradiated.
 39. The method according to claim 24 or 36, furthercomprising starting increasing the number of revolutions of thesubstrate before the radiation is irradiated, wherein the radiation isirradiated while the number of revolutions is increased.
 40. The methodaccording to claim 24 or 36, wherein the number R1 of revolutions of thesubstrate in the applying the radiation cure type resin onto thesubstrate is smaller than the number R2 of revolutions of the substratein the irradiating the radiation.
 41. The method according to claim 1,2, 24 or 36, wherein the application of the radiation cure type resinand the curing the resin are independently carried out in differentlocations.
 42. The method according to claim 24 or 36, wherein thesubstrate has a central hole, and the central hole is blocked when theradiation cure type resin is applied.
 43. The method according to claim42, wherein the block is removed from the central hole after theoptically transparent layer is formed.
 44. The method according to claim24 or 36, wherein the optically transparent layer has a thickness ofabout 0.1 mm.
 45. The method according to claim 1, 2, 24 or 36, furthercomprising forming a protective layer over the optically transparentlayer.
 46. The method according to claim 24 or 36, further comprisingforming a balance layer on a principal surface opposite to the principalsurface having the signal recording layer.
 47. The method according toclaim 46, wherein materials constituting the balance layer and theoptically transparent layer are identical in a shrinkage characteristic,and both layers have substantially the same thickness.
 48. The methodaccording to claim 46, wherein the balance layer and the opticallytransparent layer are formed by the same method.
 49. The methodaccording to claim 46, wherein the opposite principal surface has asignal recording layer.
 50. An apparatus for manufacturing an opticalinformation recording medium that comprises a substrate having a signalrecording layer formed on one principal surface thereof; and anoptically transparent layer formed on the signal recording layer andmade from a radiation cure type resin, the apparatus comprising: a unitthat supplies the radiation cure type resin; a unit that spins thesubstrate to apply or spread the radiation cure type resin; a unit thatirradiates radiation while the substrate is accelerated in spinning, toform the optically transparent layer; and a unit that suppresses thegeneration of burrs at a periphery of the substrate.
 51. The apparatusaccording to claim 50, further comprising a unit that transfers thesubstrate to another place after the application of the radiation curetype resin, wherein the unit that irradiates the radiation and the unitthat suppresses the generation of burrs are placed in the another place.52. The apparatus according to claim 50, wherein the unit thatsuppresses the generation of burrs is a member that is placed so as tobe substantially in contact with the outer end of the substrate.
 53. Theapparatus according to claim 52, wherein the member is in the shape of acord.
 54. The apparatus according to claim 52, wherein the member has atop face whose level is substantially equal to that of the principalsurface of the substrate.
 55. The apparatus according to claim 52,wherein a section of the member that is parallel to the principalsurface of the substrate is circular.
 56. The apparatus according toclaim 52, wherein the member is rotatable.
 57. The apparatus accordingto claim 56, wherein the member is rotated by the rotation force of thesubstrate.
 58. The apparatus according to claim 56, wherein the memberis rotated by a power different from a power for rotating the substrate.59. The apparatus according to claim 56, wherein the member is rotatedin the reverse direction to that of the substrate.
 60. The apparatusaccording to claim 56, wherein the member is rotated at a linear speedsubstantially equal to that of the substrate at an outer end.
 61. Theapparatus according to claim 52, further comprising a unit that removesthe radiation cure type resin which adheres to the member from themember.
 62. The apparatus according to claim 50, wherein the unit thatsuppresses the generation of burrs is a gas ejected by high pressure.63. The apparatus according to claim 50, wherein the radiation isirradiated only to the substrate.
 64. The apparatus according to claim63, wherein a shielding plate having a hole substantially equal to thesubstrate in shape is used when the radiation is irradiated.
 65. Theapparatus according to claim 50, wherein the unit that spins thesubstrate starts increasing the number of revolutions of the substratebefore the radiation is irradiated, and the unit that irradiatesradiation irradiates the radiation while the number of revolutions isincreased.
 66. The apparatus according to claim 50, wherein the numberR1 of revolutions of the substrate in the applying the radiation curetype resin onto the substrate is smaller than the number R2 ofrevolutions of the substrate in the irradiating the radiation.
 67. Theapparatus according to claim 50, wherein the substrate has a centralhole, and the apparatus comprises a member that blocks the central holebefore the radiation cure type resin is supplied.
 68. The apparatusaccording to claim 67, wherein the member that blocks is removed fromthe central hole after the optically transparent layer is formed. 69.The apparatus according to claim 50, wherein the optically transparentlayer has a thickness of about 0.1 mm.
 70. The apparatus according toclaim 50, wherein the optical information recording medium furthercomprises a protective layer formed over the optically transparentlayer.
 71. The apparatus according to claim 50, wherein the opticalinformation recording medium further comprises a balance layer formed ona surface opposite to the surface where the optically transparent layeris formed.
 72. The apparatus according to claim 71, wherein the balancelayer and the optically transparent layer are formed by the same method.73. The method according to claim 1, further comprising stopping thespinning of the substrate after application of the radiation cure typeresin in a spin coating method, wherein, after the stopping, the numberof revolutions of the substrate is increased and the radiation cure typeresin is cured.